1. Technical Field
The present disclosure relates to a board connection structure for wireless communication devices or high-frequency applied devices used in household electrical appliances.
2. Description of the Related Art
Recent higher-speed and higher-frequency wireless communication has created a demand for devices, which are essential for wireless communication, to be usable in high-frequency bands. In signal transmission in wireless communication devices or high-frequency applied devices, a coaxial cable is used for a frequency band lower than the microwave band, for example. However, at frequency bands higher than the microwave band, transmission loss is large in at least one of the dielectric and the conductor. To prevent the transmission loss, waveguides that allow low-loss transmission are widely used for the high-frequency band higher than the millimeter wave band.
A high-frequency signal can be transmitted with low loss in a circuit board for a high-frequency wave band by using a quasi-waveguide as a transmission line. The quasi-waveguide is obtained by using a layer-structure of the circuit board. Methods for taking out a signal from the circuit board to connect the circuit board to another circuit board are described in patent documents, for example. Japanese Unexamined Patent Application Publication No. 2008-131513 describes that a metal connector for waveguides is attached to a circuit board. Japanese Unexamined Patent Application Publication No. 2009-303076 describes that the openings of the waveguides are connected to each other and the circuit boards are bonded and fixed to each other.
FIG. 7 is a cross-sectional view illustrating a board connection structure described in Japanese Unexamined Patent Application Publication No. 2009-303076. In FIG. 7, a first dielectric substrate 100 and a second dielectric substrate 200 are connected and fixed through a plurality of metal bumps 300. The first dielectric substrate 100 includes a quasi-waveguide 110 that is formed of grounding conductor via holes 400, which are connected to a grounding conductor, and the dielectric. The second dielectric substrate 200 includes a quasi-waveguide 210 that is formed of grounding conductor via holes 500, which are connected to a grounding conductor, and the dielectric. The quasi-waveguide 110 and the quasi-waveguide 210 are connected by bonding the first dielectric substrate 100 and the second dielectric substrate 200 to each other.